Four hierarchical levels of peeling control in the branching adhesive setae in two Criocerinae leaf beetle species (Coleoptera, Chrysomelidae)

Abstract Representatives of the subfamily Criocerinae (Coleoptera, Chrysomelidae) possess bifid (branched) adhesive setae with spatulate and lanceolate tips, alongside non-branched climbing setae as well as male-specific setae with discoid tips. A microscopy study of the tarsal attachment systems of Crioceris asparagi (Linnaeus, 1758) and Lilioceris lilii (Scopoli, 1763) elucidates the morphology, ultrastructure, and distribution of adhesive fluid in footprints. The adhesive tips of the branched setae closely resemble those of the non-branched setae in terms of shape, dimension, and ultrastructure, producing distinct, separate double footprints. Bilobed tarsomeres are covered with setae that point disto-laterally, and their terminal branches contain internal terminal nanofibers. These components act in concert hierarchically to facilitate the dynamic shearing and double peeling associated with the beetles' attachment system. Field observations, microscopy, and morphometry analyses suggest that these beetles achieve balanced attachment and effective locomotion on the challenging surfaces of their host plants.